add plugin to monitor ARRIS TM502G cable modem

plugins/network/arris-tm502g_

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3
+# -*- python -*-
+
+# This plugin graphs the following values of the ARRIS TM502G cable
+# modem:
+#
+# * upstream and downstream powers
+# * downstream signal-to-noise ratio
+#
+# The values are retrieved from the cable modem's status web pages at
+# 192.168.100.1. So, this plugin must be installed on a munin node
+# which can access those pages.
+#
+# Symlink this plugin into the node's plugins directory (like
+# /etc/munin/plugins) as arris-tm502g_power for the powers, and
+# arris-tm502g_snr for the SNR.
+#
+# Author: Kenyon Ralph <kenyon@kenyonralph.com>
+#
+# The latest version of this plugin can be found in the munin contrib
+# repository at https://github.com/munin-monitoring/contrib. Issues
+# with this plugin may be reported there. Patches accepted through the
+# normal github process of forking the repository and submitting a
+# pull request with your commits.
+
+import html.parser
+import os
+import urllib.request
+import sys
+
+plugin_name=list(os.path.split(sys.argv[0]))[1]
+plugin_var=plugin_name.split('_', 1)[-1]
+
+if len(sys.argv) == 2 and sys.argv[1] == 'config':
+    if plugin_var == 'power':
+        print('graph_title ARRIS Cable Modem Power')
+        print('graph_vlabel Signal Strength (dBmV)')
+        print('graph_info This graph shows the downstream and upstream power reported by an ARRIS TM502G cable modem.')
+        print('downstream.label Downstream Power (dBmV)')
+        print('upstream.label Upstream Power (dBmV)')
+    if plugin_var == 'snr':
+        print('graph_title ARRIS Cable Modem SNR')
+        print('graph_vlabel Signal-to-Noise Ratio (dB)')
+        print('graph_info This graph shows the downstream signal-to-noise ratio reported by an ARRIS TM502G cable modem.')
+        print('snr.label Signal-to-Noise Ratio (dB)')
+    print('graph_category network')
+    sys.exit(0)
+
+class ArrisHTMLParser(html.parser.HTMLParser):
+    stats = list()
+    down_power = 'U'
+    up_power = 'U'
+    snr = 'U'
+    def handle_data(self, data):
+        data = data.strip()
+        if data != '' and 'dB' in data:
+            self.stats.append(data)
+    def done(self):
+        """Call this when done feeding the HTML page to the parser."""
+        self.down_power = self.stats[0].split()[0]
+        self.snr = self.stats[1].split()[0]
+        self.up_power = self.stats[2].split()[0]
+
+page = urllib.request.urlopen("http://192.168.100.1/")
+parser = ArrisHTMLParser()
+for line in page:
+    parser.feed(line.decode())
+parser.done()
+
+if plugin_var == 'power':
+    print('downstream.value ' + parser.down_power)
+    print('upstream.value ' + parser.up_power)
+    sys.exit(0)
+
+if plugin_var == 'snr':
+    print('snr.value ' + parser.snr)
+    sys.exit(0)